A plant control system comprises one or a plurality of programmable controllers, and a data sending device configured to transmit and receive data among the plurality of programmable controllers. A plurality of programs are executed inside the programmable controllers. Each program sets therein four types of variables described later, for example.
In other words, there are set a local variable which is effective only inside one program, a controller global variable which enables data to be shared among the plurality of programs inside a programmable controller, a station global variable which enables data to be shared among the plurality of programs of the plurality of programmable controllers inside a station of the data sending device, and a network variable which enables data to be shared among the plurality of programs of the plurality of programmable controllers in a plurality of stations of the data sending device.